mach-s5pv310: cpufreq smooth scaling

When a cpufreq governor policy requires to switch from a very low
frequency to a very high frequency, the low lever driver may jump to a
frequency lower than the target value requested by the higher layers,
according to the configuration of the cpufreq step up sequence.

For example, with the 2-step selection (CONFIG_FREQ_STEP_UP_L2_L0=y) a
change from L3 to L0 (500MHz to 1200MHz) would jump to 800MHz, instead
of the requested 1200MHz.

To satisfy the requirements of the higher cpufreq layers introduce a
smooth scaling mechanism that allows to switch to the target frequency
incrementally in multiple steps.

So, if it's not possible to switch to the target frequency in a single
step, schedule an additional frequency step later in the future (after
0.5sec by default) using a delayed workqueue.

The additional step is performed by the low-level driver and it's
totally transparent for the higher layers.

Signed-off-by: Andrea Righi <andrea@betterlinux.com>

arch/arm/mach-s5pv310/cpufreq.c

@@ -1157,12 +1157,36 @@ void s5pv310_set_frequency(unsigned int old_index, unsigned int new_index)
 	}
 }
 
+unsigned int target_freq_smooth;
+
+static void do_smooth_freq(struct work_struct *work)
+{
+	unsigned int target_freq;
+
+	mutex_lock(&set_cpu_freq_change);
+	target_freq = target_freq_smooth;
+	mutex_unlock(&set_cpu_freq_change);
+
+	if (likely(target_freq)) {
+		struct cpufreq_policy *policy = cpufreq_cpu_get(0);
+		int ret;
+
+		printk(KERN_INFO "%s: cpu%d: freq set to %u\n",
+			__func__, policy->cpu, target_freq_smooth);
+		ret = cpufreq_driver_target(policy,
+				target_freq_smooth, CPUFREQ_RELATION_H);
+		WARN_ON(ret < 0);
+	}
+}
+
+static DECLARE_DELAYED_WORK(smooth_freq_work, do_smooth_freq);
+
 static int s5pv310_target(struct cpufreq_policy *policy,
 		unsigned int target_freq,
 		unsigned int relation)
 {
 	int ret = 0;
-	unsigned int index, old_index;
+	unsigned int index, old_index, target_index;
 	unsigned int arm_volt;
 #ifndef CONFIG_S5PV310_BUSFREQ
 	unsigned int int_volt;
@@ -1222,6 +1246,8 @@ static int s5pv310_target(struct cpufreq_policy *policy,
 	if ((index < g_cpufreq_limit_level) && check_gov)
 		index = g_cpufreq_limit_level;
 
+	target_index = index;
+
 	if (s5pv310_max_armclk == ARMCLOCK_1200MHZ) {
 #ifdef CONFIG_FREQ_STEP_UP_L2_L0
 		/* change L2 -> L0 */
@@ -1252,6 +1278,11 @@ static int s5pv310_target(struct cpufreq_policy *policy,
 	freqs.new = s5pv310_freq_table[index].frequency;
 	freqs.cpu = policy->cpu;
 
+	if (index != target_index) {
+		target_freq_smooth = target_freq;
+		schedule_delayed_work_on(0, &smooth_freq_work, HZ >> 1);
+	}
+
 	/* If the new frequency is same with previous frequency, skip */
 	if (freqs.new == freqs.old)
 		goto bus_freq;